The invention relates to a modular instrument system for knee joint prostheses with a provisorially anchorable shaft which is provided at the distal end of a femur bone for the insertion into a bore in the direction of the anatomical axis.
A modular instrument system for knee joint prostheses is shown in U.S. Pat. No. 4,759,350 which uses a bore which is placed into the marrow cavity in the direction of the anatomical axis as an orientation aid for an instrument arrangement in which the position of the mechanical axis is determined by the transversal contact plane of the femur condyle which is perpendicular to it. For this a bar is placed into the bore along the anatomical axis at the projecting stump of which an auxiliary plate is pivotal to such an extent that it lies in contact with both femur condyles in order to fasten them afterwards with nails at the femur condyles in an angled off position for a first resection at the anterior side of the femur condyles. Then a second auxiliary plate is placed onto the just cut resection surface and oriented by means of insertable bolts to the first auxiliary plate and fixed onto this resection surface with nails in order to make a resection at the front end. The previously cut resection surfaces are in each case used as reference surfaces for the further gauges and resection blocks and abutments. An instrument set of this kind presupposes an extremely precise operating by the orthopedist, since tools are continually being changed and oriented to previously cut resection surfaces. The situation becomes even more difficult when parts of the condyles are already missing--whether due to their destruction or whether it is a matter of a re-operation--in order to determine the orientation of the mechanical axis required as an initial position.